How would you solve this basic math problem?

2/5 times 1/8

Some teachers started a hashtag #mathstratchat back on Twitter. I'd like to bring it here as well. If I can remember to do it each week. Wednesdays at 7 cantral or there about.
Check the blog or podcast here https://www.mathisfigureoutable.com/

New blog post! "Mental Math Monday" summarizing last week's question and many different calculation strategies.
#MTBoS #iTeachMath #T3Learns #MathChat #MentalMathMonday #MathStratChat #ElemMathChat #MathSky #MathsToday #ClassroomMath

Thanks to Howie Hua!!!

https://karendcampe.wordpress.com/2025/04/07/mental-math-monday/

A fun podcast I found today. Math is figureoutable
https://www.mathisfigureoutable.com/
Every Wednesday they share a mental math prompt .
Here is my solution for 16x75
#mathstratchat
Fell free to share in Twitter or Instagram if you like. I no longer go there

And on TW, Susan Russo used difference of two squares, which I hadn't thought of.
Cool!
https://twitter.com/Dsrussosusan/status/1628146466098188289?s=20

#MTBoS #iTeachMath #TryMathLive #MathEd #MathStratChat

I am happy with those 3 versions of mentally computing 83 x 97.

Please share your #ProblemSolving strategies here or on the post https://karendcampe.wordpress.com/2023/02/04/february-calendar-problems/

More #MathStratChat on Wednesdays from @pwharris
& mental math Mondays from @howie_hua

#MTBoS #iTeachMath #TryMathLive

Here's another multiplication using the area model to show double distribution.
Same four partial products as above:
80•90 + 80•7 + 90•3 + 7•3
Total = 8051

#MathStratChat #TryMathLive #MTBoS #iTeachMath #ProblemSolving #MathEd

How about decompose with a target number?

83 • 97
83•(100 – 3)
83•100 – 83•3
8300 – 249 [bc 80•3 + 3•3]
8300 – (250 – 1)
8300 – 250 + 1
8050 + 1 = 8051

#MathStratChat #TryMathLive #MTBoS #iTeachMath #ProblemSolving

Notice that I didn't say "FOIL" above... I chose to say repeated distribution since that more generally describes the math I am doing.
#WordsMatter

How else might I do this problem?

Double & halve isn't a great strategy because neither number is even.
#MathStratChat

Here is problem 1.
Reminder that for #TryMathLive I am sharing my thinking process... no need to jump in with suggestions (altho your own #ProblemSolving always welcome at the end of the thread).

#MTBoS #iTeachMath #MathStratChat
Explain how to multiply 83 x 97 using mental arithmetic.

83 x 97
My first thought is decompose & distribute:

(80 + 3)•(90 + 7)
80•90 + 3•90 + 80•7 + 3•7
7200 + 270 + 560 + 21

Now combine by place value:
7200 + 200 + 500 = 7900
70 + 60 + 21 = 151

Total = 8051

#MathStratChat #TryMathLive #MTBoS #iTeachMath #MathEd

Reminder that I posted a February Calendar of Problems from an old nctm journal. Please share w/your students or try #ProblemSolving yourself!

https://karendcampe.wordpress.com/2023/02/04/february-calendar-problems/

In this thread, I will #TryMathLive with one of the problems!
#MTBoS #iTeachMath #MathStratChat #MathEd

@davidwees @mtbos celebration of multiple methods and presentations. I found the #mathstratchat discussions some of the most engaging and empowering. #mtbos #mathed

Over on the bird site I have enjoyed a series of threads with a maths problem with the request to share your strategy - Pam Harris runs it. I can't see her on here yet.
This morning I saw the problem 4896÷96

How would you solve it?

#MathStratChat
#mathsisfun #Maths #Numbersense

@davidwees this is a good #MathStratChat prompt!
I have 3 methods:
Top: decompose & subtract by place value (mostly). Don't worry about 5–8, add -3 to other subtotal.
Middle: Number line visual
Bottom: add on 3 to both parts for easier subtraction {variations: 1008 – 998 then subtract 3; 1005 – (998+2) but must subtract 2 after, etc.} All these rely on "zero pairs" like +3 & -3.